Percussive hand tool



March 8,1927.

- R. GOLDSCHMIDT PERCUSS IVE HAND TOOL Filed Jan. 3, 1924 14 i g i z i o J i V a A l i J Iii/www.-

2 Sheets-Sheet 1 1 620,201 1 March 8 1927' R. GOLDSCHMIDT PERCUSSIVE HAND TOOL 2 Sheets-Sheet 2 Filed Jan. s,- 1924 Patented Mar. 8, 1927.,

. UNITED STATES PATENT OFFICE.

RUDOLF GOLDSCHMIDT; OF BERLIN, GERMANY, ASSIGNOR TO DET TEKNISKE FORSGS- AKTIESSKAB, OF OBDRUP, CHARLOTTENLUND, DENMARK, A COMPANY OF DEN- f um PERCUSSIVE HAND TOOL;

Application filed January 3, 1924, Serial No. 684,262, and in Germany January 17, 1928.

This invention relates to percussive hand tools of the kind in which a striking piece or tup is movable in a. casing and reclprocated by the action of one or more rotatmg flyweights mounted on the tup, the flyweights being preferably driven from an electmc motor mounted as a unit withthe tup casm %he object of the present inventionis to construct a ercussive hand'to'ol of the character descri d, which will have a striking force sufiicient for a heavy chisel or for rough ri-veting or like heavy work, without the tool being unwieldy, that is to say, w1th= out being of excessive weight oroverall dimensions.

Heretofore, in percussive hand tools of the character described, it is usual for the tup to make one blow for each revolutlon of the flyweight, but it is found that at certain speeds above a certain cr1t1cal value,

the number of impacts of the tup becomes a 4 fraction of the number of revolutions of the fl wei ht, that is to say, the tup makes one blew r each two, three, four or more revolutions of the flyweight, the number of blows per unit of time decreasing as the speed of the flyweights is increased. Not only does the number of im acts of the-tup decrease; it has been foun that'the force of the blow increases with the decrease in the number of blows of the tug increasing the speed at which t e flyweights rotate, the strength of the blow can be materially increased without increasm the weight of the tool. Ithas also been ound that in the interval between the actual working or striking strokes of the tup, the latter carries out idle strokes which do not reach the tool, the length of the working stroke being materially increased. It is therefore a further ob'ect of thisinvention to enable the increase striking force to be obtained without appreciably increasing the overall length of the tool.

According to the present invention therefore, a percussive hand tool of the charac- I ter described comprises driving or changespeed gear adapted'todrive the flyweights at such a d that the number of impacts of the tup omes a fractionof the number of revolutions of the flyweights, and driving and driven shafts splined together so as to telescope within each other to compensate so that, by

tool according to this invention. Figs. 2' and 3 are diagrams hereinafter referred to and F1 4. 1s a detail-sectional view of a.

modified construction.

Referring to Fig. 1 of the drawings, A isan electric motor mounted as aunit with be more the casing J which contains a striking piece I or tup on' which are rotatably mounted the ,flywelghts G. The motor A drives the fiywe1ghts G through a spindle E and gear- 1ng B. A spring H acts on the tupK in knownmanner to store up energy and exert a unldlrectional force on said tup. Under the combined action of the rotating flyweights G and pressure of the spring H, the I tup K exerts a blow which is transmitted to the tool T through a flexible diaphragm L 1n known manner. 1.1-;

Referring now to Fi 2 which" is a curve representing the POSltIOIl of the tup as a function of the time when the numberof blows made by 'the tup is only one thirdthe number of revolutions of the fiyweights:

-it will be seen that at 1 the tup begins to rise and at 2 has reached its highest position during the first revolution of the flyweights.

At 3 the tup begins its second upward stroke although it has not returned to its original position on line 17. This is due to the fact that the fiyweights have revolved so far during the interval that their centrifugal force overcomes the downward impulse of the tup. At 4 the tup has reached its highest position in the second revolution of the flyweights and at 5 itis again swung back by the centrifugal force "of the flyweights before it has completed its downward stroke. It then reaches its highest position at 6 and finally discharges its energy in the blow at 7. The idle strokes 3 and 5 are'of indirect utility, because they result in the effective stroke of the tap from 6 to 7 taking place in a shorter space of time and at a greater velocity, dependent on the increase in the number of idle strokes. Moreoverthe force'of impact is proportional the square of the velocity. This may also be expressed by stating that the number of idle strokes increases the inclination of the curve 6-7 which represents the working stroke, making its inclination steeper than when one blow takes lace for each' revolution of the flyweig ts. Without going deeply into the complex theory of the physical operations the accumulation of energy may be explainedas follows :-The impulse of the working, or effective stroke (mean striking force multiplied by the time of the blow) is equal to the rearward impulse on the casing or operators hand. The time of the rearward impulse increases according to the number of idle strokes and consequently the impulse inherent in the blow also increases.

It will be apparent from the foregoing remarks that the force of impact of the tup Y can be multiplied considerably without increasing the weight of the tool.

It is however essential that the speed of the flyweights should be kept fairly constant. This will be apparent from the curve I of Fig. 3 wherein the force of impact in mkg. (meterkilograms) is represented for different revolutions (per unit of time) of the fl weight and wherein A represents one b ow per revolution, B one blow for two revolutions and C one blow for each three revolut-ions of the flyweights and wherein a, a and a represent different revolutions per unit of time of the fiyweights where no impact takes place. In order to ensure steady o oration when an electric motor is em- {1 oyed, it is necessary that the motor should ave a rapidly decreasing speed characteristic torque as a function of the number of revo utions). A shunt motor which has a constant s eed, might, for example, run at the speed indicated by one of the points a, a or a where the impact of the tup is zero. It will therefore be preferable to employ a series-motor or a shunt motor wherein a decreasing speed charactenstic is produced by compounding or inserting a resistance in the armature circuit. In the case of induction motors it would be necessary to provide a comparatively high rotor resistance.

The torque curve II of Fig. 3 intersects the curve I at b and it will therefore be seen that the operation of the tool at this point would be steady and that the flyweights should therefore preferably be run at a speed of a revolutions per unit of time. The speedof the motor may be varied to regulate t e timing of the tup impacts.

The increase in the force of impact of the tup however also involves a longer stroke and it would be necessary therefore to increase the length of the tool casing. In order to obviate this necessity the motor or driving shaft may be made hollow to receive and guide the driven spindle of the geari eeoator ing, thus reducing the overall length of the tool and'also doing away with a special bearing for the gear spindle, as the motor shaft will serve to support the gear spindle. Such a construction is shown in Fig. 1 wherein the motor shaft W is hollow and keyed to the hub D of a flange or disc M which is integral with or secured to a casing or box having a cylindrical wall N and a lower disc or bottom U. A sleeve P on a spindle E which passes through the box or casing N, is resiliently connected to the box N by a resilient transmission device, such as a spring Y or other resilient coupling. The sleeve 1? is splined on the spindle E by means of a key or feather working in the groove E in the spindle E and the spindle extends into the hollow motor shaft W, which forms a bearing for the spindle E. It will be understood that the motor shaft W rotates the box or casing N and that the rotary motion is resiliently transmitted to the sleeve P-through the spring Y. The sleeve P thus rotates the spindle E which carries one of the pinions B, whilst the spindle E is free to reciprocate in the hollow motor shaft W under the reciprocation of the tu and its gearing B. Fig. 1 shows the spin le E almost up to the end of the socket in the hollow shaftW.

Fig. 4 shows a modification wherein rollers S carried in a roller cage H are inserted between the flywei hts G and their journal pins F. It will 0 course be understood that balls or other anti-friction devices may be used in place of the rollers. This construction facilitates the operation of the tool by reducing the frictional resistance to revolution of the flyweights at a high speed.

Claims- 1. A percussive hand tool of the character described, comprising a casing, an electric motor mounted as a unit therewith, a shaft driven by said motor, a tup movable in said casing, a flyweight rotatably mounted on the tup, a driven shaft splined to the aforesaid shaft, whereby said shafts are telescopic, and gearin interposed between said driven shaft and ywcight whereby the number of impacts of the tup becomes a fraction of the number of revolutions of the fiyweight.

2. A percussive hand tool of the character described, comprising a casing, a tup movable therein, a flyweight rotatably mounted till on the tup. an electric motor mounted as a I lift able therein, a flyweight rotatably mounted on the tup, an electric motor mounted as 'a unit axially within said casing, a driving of the tup becomes a fraction of the number of revolutions of the flfiveight and a resilient transmission device interposed 'between the driving shaft and the flyweight.

In testimony whereof I hereunto aflix my signature.

RUDOLF GOLDSCHMIDT. 

